Nov. 2, 2010 --The human papillomarvirus (HPV) shot is a cost-effective way to prevent genital warts and anal cancer in men who have sex with men. This is the finding of a new study that appears in The Lancet.

In 2010, there will be about 5,260 new cases of anal cancer diagnosed in the U.S, and about 720 people will die from this disease, according to the American Cancer Society. There are no routine prevention programs or screening tests for anal cancer.

HPV vaccines protect against certain types of HPV that are linked to cervical cancer and anal cancer. A sexually transmitted disease, HPV or genital warts can be transmitted through vaginal, anal, and oral sex. Nearly 80% of cases of anal cancer are linked to two of the types of HPV that the vaccine targets.

Vaccines for High-Risk Men

Jane J Kim, PhD, an assistant professor of health decision science in the department of health policy and management at the Harvard School of Public Health in Boston, constructed models to assess the cost-effectiveness of the HPV shot across a range of potential scenarios involving men who have sex with men. The scenarios were based on age, previous exposure to the types of warts that are targeted by the vaccine, and HIV status. Men who test positive for HIV, the virus that causes AIDS, are at higher risk for HPV and anal cancer.

Researchers used measurements called "QALY." QALY -- which stands for "quality adjusted life year" -- is a measurement of both quality and length of life. In the study, a cost-effectiveness ratio of less than $50,000 per QALY gained is considered a "good value for money."

Vaccinating men who have sex with other men against HPV between the ages of 12 to 26 is a cost-effective strategy, Kim concludes. If further study shows that this vaccine is also effective against HPV-related cancers it may be an even more cost-effective intervention.

Who Should Get the HPV Shot?

Casting a wide net -- routine vaccination of all men and boys -- may not be the best way to prevent anal cancer and genital warts in this high-risk group, Kim writes. Instead, targeting men who have sex with men between the ages of 12 and 26 may be the way to go, she says.

"Such a strategy is very likely to be a valuable health investment for a high-risk population that otherwise relies on no other organized prevention strategy against an illness with a high disease burden," she writes.

Younger men may not be aware of their sexual identity or willing to disclose it, and this is one of the reasons some experts were calling for routine vaccination of all boys.

"Programs targeting HPV vaccination of males who have sex with other males at older ages -- when more men have established and are willing to disclose their sexual identity -- might be a good approach to reach this high-risk group," she says.

Vaccine Programs

"The risk of anal cancer is higher in men who have sex with other men, and there is no routine screening program in place," says Joel Palefsky, MD, a professor of medicine at the University of California at San Francisco. He wrote an editorial accompanying the new study.

"From a health standpoint, it is clear that this vaccine works pretty well to prevent anal warts and likely anal cancer," he tells WebMD. "The implementation of a vaccination program would be the only organized prevention effort available."

Some of the details still need to be worked out.

"Most men who have sex with men will not be self-identified or have identified themselves to their primary care providers at the age of 12, and we would hope males would be vaccinated as early as possible," Palefsky says.

That said, "the vaccine would be cost-effective up to the age of 26 when a much bigger chunk of men who have sex with men would be self-identified," he says.

Vaccine Recommendations

"I am optimistic that FDA and the Advisory Committee on Immunization Practices (ACIP) will agree that anal cancer is a worthwhile indication for this vaccine in men and women, and the real question is should it be recommended for routine use in boys," Palefsky says.

"The vaccine won't get serious uptake in males unless it is included in the routine vaccine schedule, but my crystal ball is not clear enough to predict that at this time," he says. The ACIP, which advises the CDC on vaccine matters, is currently reviewing the data and expected to make its recommendations soon.

Two HPV vaccines are now licensed by the FDA and recommended by CDC -- Cervarix and Gardasil.

These vaccines are now on the CDC's routine childhood vaccine schedule for girls aged 9 to 26. Gardasil is licensed for males aged 9 through 26.

"This is a rare cancer-prevention opportunity where anal cancer is known to be associated with HPV and we have a vaccine available against the virus," says Jaffer A. Ajani, MD, a professor of medicine in the department of gastrointestinal oncology at MD Anderson Cancer Center in Houston. "However, the challenge is in implementing the strategy," he says. "Complexities lie in identifying the relevant population and motivating them to accept immunization."

"Anal cancer is an important condition, but not a prevalent one," says Abby Lippman, PhD, a professor of epidemiology at McGill University in Montreal. "The cost-effectiveness data is good to see, but that is a secondary issue. We need to figure out what our public health priorities are, and how best to address them," she says.

"Merely having what some allege to be a 'magic bullet,' -- and still much is not known about the vaccine given how new it is, and how almost all the data has been sponsored by the companies manufacturing it -- doesn't mean we go out and shoot." Lippman publically criticized Canada for rushing to include Gardasil in their routine immunization schedule.